Known from the German Laid Open Print 27 34 249 is a hip joint acetabular prosthesis of this type where the connecting part forms a single-piece head part with the spherical head and displays at its shaft side end a socket cone capable of being pushed into and fixed in a corresponding conical boring of the shaft. This known two-part construction of head and shaft has the advantage of a flexible adaptation of head size and shaft size to the patient data, with a comparably surveyable inventory. If certain shaft sizes and head parts are kept ready, the operator can then select, even during the operation, rapidly the suitable head and shaft combination. Additionally, the head part, consisting of head and connecting part, can be aligned independently of the final position of the shaft and then fixed.
Besides shaft size and head size, still further strongly patient-dependent, as a rule, is the so-called CCD-angle that the shaft axis forms with the shank neck axis running through the head center point and the adjacent shank neck, and crossing the shaft axis. This CCD-angle in the case of the natural femur on the average lies at approximately 126.degree., with a width of variation between 115.degree. and 140.degree.. In the case of the two-piece hip joint acetabular prosthesis in accordance with the German Laid Open Print 27 34 249, the CCD-angle is obtained by approximate curving of the single-piece connecting part formed at the head; the selection of a suitable CCD-angle and the selection of a required head size that is independent thereof is, therefore, not possible in the case of this known hip joint femoral prosthesis. A somewhat sufficient adaptation of CCD-angle and head size to the patient data, much more to the point, can, in the case of this known hip joint femoral prosthesis, only be realized by maintaining in stock (inventory) for each head size a plurality of head parts with different CCD-angles. Therefore, the operator must, e.g. during an operation, select from a large number of different head parts the one displaying the correct head size and, additionally, the correct CCD-angle.
Known from the German Laid Open Print 33 40 767 is an assembly made up of several piece parts that can be put together into a hip joint acetabular prosthesis of desired length, whereby the piece parts inserted between the shaft and the head each display, on the shaft side, a conical boring and, on the head side, each a corresponding conical stub in order to enable a simple assembly of the hip joint femoral prosthesis. The task set forth for the invention is to further develop the hip joint femoral prosthesis of the initially mentioned art such that adaptation of the CCD-angle of the femoral prosthesis to patient requirements is possible in simple fashion, independently of the selected size of prosthesis head and of prosthesis shaft.
This task is resolved in the present case of the hip joint femoral prosthesis.
The advantages of the invention lie, in particular, in the fact that the hip joint femoral prosthesis has, between the shaft and the head, a separate connecting part that serves for realizing the patient-correct, desired CCD-angle and, additionally, enables a linkage-correct alignment of the head by appropriate rotation of the connecting part in the conical boring of the shaft, and subsequent fixing. By suitable selection of shaft size, of the angled connecting part and of the head size, capable of being realized is a hip joint femoral prosthesis that is easily adaptable to the individual patient data, if these three parts are stocked in appropriately sized steps. By this means, inventory remains capable of being surveyed, and the selection of the parts required for realizing the individually fitted femoral prosthesis is relatively surveyable and simple for the operator-even during an operation.
Advantageously, the two socket cones have, at both ends of the connecting part, the same dimensions and the conical borings at the proximal end of the shaft, respectively in the head, are then likewise constructed the same, so that mixing up the socket cones leads to no problems.
Particularly preferred, the conical boring in the proximal end of the shaft runs at a predetermined angle of .alpha.(alpha)&lt;180.degree. to the shaft axis, with the conical boring then being made in a region of the shaft that retains about the conical boring the greatest possible wall thickness and, therewith, the greatest possible wall strength. With this form of embodiment of the invention, the CCD-angle is obtained by the difference between the angle and .beta. (beta). Particularly preferred, the conical boring of the shaft runs at an angle .alpha..apprxeq.140.degree. (alpha approximately equal) to the shaft axis, and the angle .beta. (beta) between the two socket cones of the connecting part then lies, for realizing a CCD-angle of 140.degree. to 110.degree., in the region of 0.ltoreq..beta..ltoreq.30.degree. (zero is less than or equal to beta and beta is less than or equal to 30.degree.).